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I am running Ubuntu 19.10 on a Lenovo ThinkPad X1 Tablet Gen 3 connected to a Lenovo Thunderbolt 3 Dock 40AF. On the dock connections, everything (Ethernet, USB, Charging) works, but only HDMI and DisplayPort connections will not.

I have tried the standard tricks of enabling and disabling the Thunderbolt access in the Gnome UI and I have also been following this tutorial. Strang thing is that boltctl command will not yield any output. I have been looking for log files, etc. but not found anything that would give me further information.

I cannot (and also do not want to) disable the BIOS security features.

Any further input what to do?

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Thunderbolt 3 is a tunnelling protocol that can transport PCIe and DisplayPort data. A bit confusingly, Thunderbolt is one of the "alternate modes" of the USB type C port. Besides Thunderbolt and USB 3, the port itself can also directly act as DisplayPort and HDMI port (amongst others). See the schema from anandtech.

When used with a Thunderbolt device, the PCIe tunnels are only created once the device is authorized, unless security is disabled. This is done via bolt and the kernel. But the DisplayPort streams do not require authorization and should always work. The same is true for DisplayPort alternate mode in case a DisplayPort device is directly connected to the USB Type C.

That you see no output via boltctl and the type specifier for the dock (40AF) makes me believe that you have indeed the ThinkPad Hybrid USB-C dock, which is not a Thunderbolt dock. In that case the DisplayPort/HDMI of the dock use DisplayLink and thus likely need an additional driver.

NB: Logs for bolt can easily be obtained via journalctl -b -u bolt but I am pretty sure bolt is not in the mix here.

  • thanks. Indeed your observation was correct. The Hybrid Dock ist not a Thunderbold dock.... Will install the displaylink driver. – sebicm Nov 27 '19 at 7:03

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